IdMessageCoder.pas contains types, classes, and variables used to define the ancestor classes for Indy coders and decoders that handle RFC-822 compliant message parts. Most IdMessageCoder.pas classes define the framework for the descendant classes. Specific encoder and decoder implements can be found in other Indy units, including IdMessageCoderMIME.pas, IdMessageCoderUUE.pas, and IdMessageCoderXXE.pas.